Fix alpha sqrt fegetenv namespace (bug 20768).

On alpha, sqrt (a C90 function) brings in references to fegetenv
(C99), resulting in linknamespace test failures:

[initial] __sqrt -> [libm.a(w_sqrt.o)] __ieee754_sqrt ->
[libm.a(e_sqrt.o)] __feholdexcept -> [libm.a(feholdexcpt.o)] fegetenv

This patch fixes this by making __feholdexcept call __fegetenv instead
of fegetenv.

Tested for Alpha (compilation only).

	[BZ #20768]
	* sysdeps/alpha/fpu/feholdexcpt.c (__feholdexcept): Call
	__fegetenv instead of fegetenv.